Projectile fragmentation of [sup.40,48]Ca and isotopic scaling in a transport approach

We investigate theoretically projectile fragmentation in reactions of [sup.40,48]Ca on [sup.9]Be and [sup.181]Ta targets using a Boltzmann-type transport approach, which is supplemented by a statistical decay code to describe the de-excitation of the hot primary fragments. We determine the thermodynamical properties of the primary fragments and calculate the isotope distributions of the cold final fragments. These describe the data reasonably well. For the pairs of projectiles with different isotopic content we analyze the isotopic scaling (or isoscaling) of the final fragment distributions, which has been used to extract the symmetry energy of the primary source. The calculation exhibits isoscaling behavior for the total yields as do the experiments. We also perform an impact-parameter-dependent isoscaling analysis in view of the fact that the primary systems at different impact parameters have very different properties. Then the isoscaling behavior is less stringent, which we can attribute to specific structure effects of the [sup.40,48]Ca pair. The symmetry energy determined in this way depends on these structure effects.